We are examining the past exposure to lead in 250 well characterized children with ADHD, and a suitable group of controls. Our measure of past exposure is bone lead levels obtained by XRay fluorescence spectroscopy, a relatively new way of estimating bone lead concentrations, and by inference, body lead burdens. By comparing the lead concentrations in these two groups, controlling for other factors which could confound, we will estimate odds ratios for ADHD given elevated bone lead, and estimate the contribution of lead to this disease of childhood.